1 INTRODUCTION
An integral pan of the licensing procedure for the potential nuclear waste repository at Yucca Mountain, Nevada, involves accurate prediction of the in-situ rheology for design and construction of the facility and emplacement of the canisters containing radioactive waste. The data required as input to successful thermal and mechanical models of the behavior of the repository and surrounding lithologies include bulk density, grain density, porosity, compressional and shear wave velocities, elastic moduli, and compressional and tensile strengths. In this study a suite of experiments was performed on cores recovered from the USW-NRG-6 borehole drilled to support the Exploratory Studies Facility (ESF) at Yucca Mountain. USW-NRG-6 was drilled to a depth of 1100 feet through four thermal/mechanical units of Paintbrush tuff. The thermal/mechanical stratigraphy was defined by Oritz et al (1985) to group rock horizons of similar properties for the purpose of simplifying modeling efforts. The tuff samples from USW-NRG-6 have a wide range of welding characteristics (usually reflected in sample porosity) and a small range of mineralogy and petrology characteristics. Generally samples are silicic ashfall tuffs that exhibit large variability in their elastic and strength properties (see Price and Bauer, 1985). The four thermal/mechanical units are designated: TCw, a relatively low porosity welded tuff; PTn, a non-welded very porous tuff sometimes having a high percentage of zeolites and clay; TSw1, a lithophysal rich and vapor-phase altered welded tuff; and TSw2 (the potential repository horizon), a welded tuff with relatively few lithophysal cavities and vapor-phase altered zones.
These data constitute a substantial data set to establish correlations between the fracture strength, bulk properties, and elastic properties of the tuff. The emphasis in this study is to collect as much data as possible, in a more or less routine way, on the potential repository horizon and surrounding thermal/mechanical units.
